This invention relates to a combination check and relief valve having broad application in fluid transfer systems, one being the installation on the discharge side of centrifugal pumps. Pumps of this type frequently are left running while the flow through them is blocked by closing valves downstream. Leaving a centrifugal pump running over an extended period of time causes the fluid to be heated to unacceptably high temperatures by the mechanical action of the pump on the fluid, thereby damaging the pump seals.
Frequently, it is desirable to install a check valve in a fluid transfer system to provide positive protection against back-flow. This is particularly true when there is a centrifugal pump in the system, since fluid can back-flow through the pump clearances while the pump is stopped.
In the past, it has been common to install two separate devices to provide for pump by-pass and positive back-flow protection, which may be unacceptably expensive.
In the prior-art, there have been attempts to produce combination by-pass and check valves. However, these valves have had several inherent disadvantages. The internal construction of these valves has tended to be rather complex, resulting in the combination valve being relatively expensive to manufacture. Also, because of this complex construction, it has been relatively difficult to alter the flow rate through the by-pass line. Furthermore, the fluid flow path through these valves has tended to be rather tortuous, thereby causing excessive pressure drop through the valve and increasing the possibility of pluggage from impurities in the fluid.
In is an object of this invention to provide a relatively inexpensive, reliable combination by-pass and check valve having a low pressure drop from the inlet to the outlet.
It is a further object to provide a combination by-pass and check valve in which the flow rate through the by-pass can be altered relatively easily.
The subject invention comprises a valve having a seat between the inlet and outlet on which rests a check disc to block reverse flow. A tubular by-pass located in the valve body intermediate the inlet and the seat comprises a radially extending tubular section and a perforate, tubular section. A sleeve integral with, and extending from the disc concentric with the perforate tubular section has one or more orifices therethrough and a circumferential recess therein. When valves downstream of the subject invention are closed to prevent fluid flow while the pump is running, the disc is seated. All fluid entering the valve passage from the inlet flows through orifices in the sleeve, into the sleeve recess, and finally through the perforations in the perforate tubular section into the by-pass. When the downstream valves are opened slightly, a portion of the fluid will flow from the inlet to the outlet, thereby moving the disc slightly off its seat, while the remaining fluid will flow through into the by-pass as previously described. As the rate of fluid flow is increased through the valve passage from the inlet to the outlet by opening the downstream valves still further, the disc is increasingly moved away from it seat, threby further moving the sleeve. This movement of the sleeve enventually results in the orifices and circumferential recess in the sleeve being totally non-aligned, non-communicating with the perforations in the tubular section, thereby preventing any flow through the by-pass.